Transmission method and apparatus for mapping downlink control information and transmitting a mapped downlink control signal

ABSTRACT

In the base station (100), a search space setting unit (103) sets a search space on the basis of a search space setting rule in accordance with R-PDCCH range of a setting target slot, and an allocating unit (108) places DCI in one of a plurality of candidates of to-be-decoded unit range included in the set search space. The search space setting rules are associated with respective numbers of candidates of to-be-decoded unit range corresponding to the respective ones of a plurality of numbers of connections for R-CCE, and a first search space setting rule of a slot 0 and a second search space setting rule of a slot 1 are different from each other in terms of the patterns related to the numbers of candidates of to-be-decoded unit range corresponding to the plurality of numbers of connections for R-CCE.

RELATED APPLICATIONS

This continuation application claims priority to U.S. patent applicationSer. No. 15/883,760 filed Jan. 30, 2018; U.S. patent application Ser.No. 15/478,701, filed Apr. 4, 2017, which claims priority to U.S. patentapplication Ser. No. 15/369,139, filed Dec. 5, 2016, which claimspriority to U.S. patent application Ser. No. 14/830,007, filed Aug. 19,2015, which claims priority to U.S. patent application Ser. No.14/656,245, filed Mar. 12, 2015, which claims priority to U.S. patentapplication Ser. No. 13/810,817, filed Jan. 17, 2013, andPCT/JP2011/003900, filed Jul. 7, 2011, the entireties of which areincorporated herein by reference.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims priority from Japanese Patent Application No.2010-164309, filed Jul. 21, 2010. The contents of this application areherein incorporated by reference.

TECHNICAL FIELD

The claimed invention relates to a base station, a terminal, atransmission method and a reception method.

BACKGROUND ART

In 3rd Generation Partnership Project Radio Access Network Long TermEvolution (3GPP-LTE (hereinafter referred to as LTE)), OrthogonalFrequency Division Multiple Access (OFDMA) is adopted as a downlinkcommunication scheme, and Single Carrier Frequency Division MultipleAccess (SC-FDMA) is adopted as an uplink communication scheme (e.g., seeNPL-1, NPL-2, and NPL-3).

In LTE, a base station apparatus for radio communications (hereinafterabbreviated as “base station”) performs communications by allocating aresource block (RB) in a system band to a terminal apparatus for radiocommunications (hereinafter abbreviated as “terminal”) for every timeunit called “subframe.” The base station also transmits allocationcontrol information (i.e., L1/L2 control information) for thenotification of the result of resource allocation of downlink data anduplink data to the terminal. The allocation control information istransmitted to the terminal through a downlink control channel such as aPhysical Downlink Control Channel (PDCCH). A resource region to which aPDCCH is to be mapped is specified. As shown in FIG. 1, a PDCCH coversthe entire system bandwidth in the frequency-domain and the regionoccupied by the PDCCH in the time-domain varies between a leading firstOFDM symbol and a third OFDM symbol in a single subframe. A signalindicating a range of OFDM symbols occupied by a PDCCH in thetime-domain direction is transmitted through a Physical Control FormatIndicator Channel (PCFICH).

Each PDCCH also occupies a resource composed of one or more consecutivecontrol channel elements (CCEs). In a PDCCH, one CCE consists of 36resource elements (RE). In LTE, the number of CCEs occupied by a PDCCH(CCE aggregation level, or simply aggregation level) is selected from 1,2, 4, and 8 depending on the number of bits of allocation controlinformation or the condition of a propagation path of a terminal. In LTEa frequency band having a system bandwidth of up to 20 MHz is supported.

Allocation control information transmitted from a base station isreferred to as downlink control information (DCI). If a base stationallocates a plurality of terminals to one subframe, the base stationtransmits a plurality of items of DCI simultaneously. In this case, inorder to identify a terminal to which each item of DCI is transmitted,the base station transmits the DCI with CRC bits included therein, thebits being masked (or scrambled) with a terminal ID of the transmissiondestination terminal. Then, the terminal performs demasking (ordescrambling) on the CRC bits of a plurality of items of possible DCIdirected to the terminal with its own ID, thereby blind-decoding a PDCCHto detect the DCI directed to the terminal.

DCI also includes resource information allocated to a terminal by a basestation (resource allocation information) and a modulation and channelcoding scheme (MCS). Furthermore, DCI has a plurality of formats foruplink, downlink Multiple Input Multiple Output (MIMO) transmission, anddownlink non-consecutive band allocation. A terminal needs to receiveboth downlink allocation control information (i.e., allocation controlinformation about a downlink) and uplink allocation control information(i.e., allocation control information about an uplink) which have aplurality of formats.

For example, for the downlink allocation control information, formats ofa plurality of sizes are defined depending on a method for controlling atransmission antenna of a base station and a method for allocating aresource. Among the formats, a downlink allocation control informationformat for consecutive band allocation (hereinafter simply referred toas “downlink allocation control information”) and an uplink allocationcontrol information format for consecutive band allocation (hereinaftersimply referred to as “uplink allocation control information”) have thesame size. These formats (i.e., DCI formats) include type information(for example, a one-bit flag) indicating the type of allocation controlinformation (downlink allocation control information or uplinkallocation control information). Thus, even if DCI indicating downlinkallocation control information and DCI indicating uplink allocationcontrol information have the same size, a terminal can determine whetherspecific DCI indicates downlink allocation control information or uplinkallocation control information by checking type information included inallocation control information.

The DCI format in which uplink allocation control information forconsecutive band allocation is transmitted is referred to as “DCI format0” (hereinafter referred to as “DCI 0”), and the DCI format in whichdownlink allocation control information for consecutive band allocationis transmitted is referred to as “DCI format 1A” (hereinafter referredto as “DCI 1A”). Since DCI 0 and DCI 1A are of the same size anddistinguishable from each other by referring to type information asdescribed above, hereinafter, DCI 0 and DCI 1A will be collectivelyreferred to as DCI 0/1A.

In addition to these DCI formats, there are other formats for downlink,such as DCI format 1 used for non-consecutive band allocation(hereinafter referred to as DCI 1) and DCI formats 2 and 2A used forallocating spatial multiplexing MIMO transmission (hereinafter referredto as DCI 2 and 2A). DCI 1, DCI 2, and DCI 2A are formats that aredependent on a downlink transmission mode of a terminal (non-consecutiveband allocation or spatial multiplexing MIMO transmission) andconfigured for each terminal. In contrast, DCI 0/1A is a format that isindependent of the transmission mode and can be used for a terminalhaving any transmission mode, i.e., a format commonly used for everyterminal. If DCI 0/1A is used, single-antenna transmission or a transmitdiversity scheme is used as a default transmission mode.

Also, for the purpose of reducing the number of blind decodingoperations to reduce a circuit scale of a terminal, a method forlimiting CCEs targeted for blind decoding for each terminal has beenunder study. This method limits a CCE region that may be targeted forblind decoding by each terminal (hereinafter referred to as “searchspace”). As used herein, a CCE region unit allocated to each terminal(i.e., corresponding to a unit for blind decoding) is referred to as“downlink control information allocation region candidate (i.e., DCIallocation region candidate)” or “unit region candidate targeted fordecoding.”

In LTE, a search space is configured for each terminal at random. Thenumber of CCEs that form a search space is defined per CCE aggregationlevel of a PDCCH. For example, as shown in FIG. 2, the numbers of CCEsforming search spaces are 6, 12, 8, and 16 for PDCCH CCE aggregationlevels 1, 2, 4, and 8, respectively. In this case, the numbers of unitregion candidates targeted for decoding are 6 (=6/1), 6 (=12/2), 2(=8/4), and 2 (=16/8) for PDCCH CCE aggregation levels 1, 2, 4, and 8,respectively (see FIG. 3). In other words, the total number of unitregion candidates targeted for decoding is limited to 16. Thus, sinceeach terminal may perform blind-decoding only on a group of unit regioncandidates targeted for decoding in a search space allocated to theterminal, the number of blind decoding operations can be reduced. Asearch space in each terminal is configured using a terminal ID of eachterminal and a hash function for randomization. A terminal-specific CCEregion is referred to as “UE specific search space (UE-SS)”.

The PDCCH also includes control information for data allocation, theinformation being common to a plurality of terminals and notified to theplurality of terminals simultaneously (for example, allocationinformation about downlink broadcast signals and allocation informationabout signals for paging) (hereinafter referred to as “controlinformation for a shared channel”). To transmit the control informationfor a shared channel, a CCE region common to all the terminals that areto receive downlink broadcast signals (hereinafter referred to as“common search space: C-SS”) is used for the PDCCH. A C-SS includes justsix unit region candidates targeted for decoding in total, namely, 4(=16/4) and 2 (=16/8) candidates for CCE aggregation levels 4 and 8,respectively (see FIG. 3).

In a UE-SS, the terminal performs blind-decoding for the DCI formats oftwo sizes, i.e., the DCI format (DCI 0/1A) common to all the terminalsand the DCI format (one of DCI 1, DCI 2 and DCI 2A) dependent on thetransmission mode. For example, in a UE-SS, the terminal performs 16blind-decoding operations for each of the DCI formats of the two sizesas described above. A transmission mode notified by the base stationdetermines for which two sizes of the DCI formats the blind decoding isperformed. In contrast, in a C-SS, the terminal performs sixblind-decoding operations on each of DCI format 1C, which is a formatfor shared channel allocation (hereinafter referred to as “DCI 1C”) andDCI 1A, (i.e., 12 blind decoding operations in total) regardless of anotified transmission mode.

DCI 1A used for shared channel allocation and DCI 0/1A used forterminal-specific data allocation have the same size, and terminal IDsare used to distinguish between DCI 1A and DCI 0/1A. Thus, the basestation can transmit DCI 0/1A used for terminal-specific data allocationin a C-SS as well without an increase in the number of blind decodingoperations to be performed by the terminals.

Also, the standardization of 3GPP LTE-Advanced (hereinafter referred toas LTE-A), which provides a data transfer rate higher than that of LTE,has been started. In LTE-A, in order to achieve a downlink transfer rateof up to 1 Gbps and an uplink transfer rate of up to 500 Mbps, basestations and terminals (hereinafter referred to as LTE-A terminals)capable of communicating at a wideband frequency of 40 MHz or higherwill be introduced. An LTE-A system is also required to supportterminals designed for an LTE system (hereinafter referred to as LTEterminals) in the system in addition to LTE-A terminals.

In LTE-A, a new uplink transmission method will be introduced that usesa non-consecutive band allocation and MIMO. Accordingly, the definitionsof new DCI formats (e.g., DCI formats 0A and 0B (hereinafter referred toas DCI 0A and DCI 0B)) (e.g., see NPL-4) are being studied. In otherwords, DCI 0A and DCI 0B are DCI formats that depend on the uplinktransmission mode.

As described, in LTE-A, if a DCI format (any one of DCI 1, DCI 2, andDCI 2A) dependent on the downlink transmission mode, a DCI formatdependent on the uplink transmission mode (any one of DCI 0A and DCI0B), and a DCI format independent of the transmission mode and common toall the terminals (DCI 0/1A) are used in UE-SS, then the terminalperforms blind-decoding (monitoring) on DCI of the abovementioned threeDCI formats. For example, as described above, since a UE-SS needs 16blind decoding operations per DCI format, the total number of blinddecoding operations in the UE-SS is 48 (=16×3). Accordingly, 60 blinddecoding operations in total is needed after adding 12 (=6×2), i.e., thenumber of blind decoding operations for the two DCI formats in the C-SS.

Additionally, in LTE-A, to achieve an increased coverage, theintroduction of radio communication relay apparatus (hereinafterreferred to as “relay station” or “Relay Node” (RN)) has been specified(see FIG. 4). Accordingly, the standardization of downlink controlchannels from base stations to relay stations (hereinafter referred toas “R-PDCCH”) is under way (e.g., see NPL-5, NPL-6, NPL-7, and NPL-8).At present, the following matters are being studied in relation to theR-PDCCH. FIG. 5 illustrates an example of an R-PDCCH region.

(1) A mapping start position in the time-domain of an R-PDCCH is fixedat the fourth OFDM symbol from the beginning of a subframe, and thusdoes not depend on the rate at which a PDCCH occupies OFDM symbols inthe time-domain.

(2) As a mapping method in the frequency-domain of an R-PDCCH, twodisposing methods, “localized” and “distributed” are supported.

(3) As reference signals for demodulation, Common Reference Signal (CRS)and Demodulation Reference Signal (DM-RS) are supported. The basestation notifies the relay station as to which reference signal is used.

(4) Each R-PDCCH occupies a resource composed of one or more consecutiveRelay-Control Channel Elements (R-CCEs). The number of REs forming oneR-CCE varies for each slot, or for each reference signal location.Specifically, in slot 0, a R-CCE is defined as a resource region having,in the time direction, a range of from the third OFDM symbol to the endof slot 0, and having, in the frequency direction, a range of 1 RB'swidth (excluding, however, the region onto which the reference signal ismapped). In addition, in slot 1, a R-CCE is defined as a resource regionhaving, in the time direction, a range of from the beginning of slot 1to the end of slot 1, and having, in the frequency direction, a range of1 RB's width (excluding, however, the region onto which the referencesignal is mapped). However, proposals have also been made to divide theabove-mentioned resource region into two in slot 1, and to have each beone R-CCE.

CITATION LIST Non-Patent Literature

-   NPL 1: 3GPP TS 36.211 V9.1.0, “Physical Channels and Modulation    (Release 9),” May 2010-   NPL 2: 3GPP TS 36.212 V9.2.0, “Multiplexing and channel coding    (Release 9),” June 2010-   NPL 3: 3GPP TS 36.213 V9.2.0, “Physical layer procedures (Release    9),” June 2010-   NPL 4: 3GPP TSG RAN WG1 meeting, R1-092641, “PDCCH design for    Carrier aggregation and Post Rel-8 feature,” June 2009-   NPL 5: 3GPP TSG RAN WG1 meeting, R1-102700, “Backhaul Control    Channel Design in Downlink,” May 2010-   NPL 6: 3GPP TSG RAN WG1 meeting, R1-102881, “R-PDCCH placement,” May    2010-   NPL 7: 3GPP TSG RAN WG1 meeting, R1-103040, “R-PDCCH search space    design,” May 2010-   NPL 8: 3GPP TSG RAN WG1 meeting, R1-103062, “Supporting frequency    diversity and frequency selective R-PDCCH transmissions,” May 2010

SUMMARY OF INVENTION Technical Problem

It is anticipated that resources for a resource region to which a PDCCHfor a terminal under the control of a base station is mapped(hereinafter referred to as “PDCCH region”) may become insufficient insome cases. One potential method for addressing this resource shortageis to dispose the DCI for the terminal under the control of the basestation in the resource region to which the R-PDCCH is mapped(hereinafter referred to as “R-PDCCH region”) (see FIG. 6).

However, simply adding an R-PDCCH region to a PDCCH region as a resourceregion for transmitting DCI to a terminal connected to a base stationmay disadvantageously lead to an increase in the number of blinddecoding operations to be performed by the terminal, resulting inincreases in power consumption, processing delay, and circuit scale. Forexample, according to the above-described configuration of a searchspace, in one subframe, a search space is configured for each of a PDCCHregion, an R-PDCCH region of slot 0, and an R-PDCCH region of slot 1.Thus, if the number of blind decoding operations to be performed by aterminal in each region is 60 as mentioned above, the terminal wouldrepeat 180 blind decoding operations (=60×3 regions) in total for eachsubframe. In other words, the number of blind decoding operationsincreases and the configuration of a terminal becomes complicated.

Also, another possible configuration method might be one where a searchspace is allocated to each of a PDCCH region and R-PDCCH regions (slot 0and slot 1) in such a manner that the total number of region candidatesfor blind decoding (i.e., the total number of blind decoding operations)by a terminal in one subframe is made to be generally comparable to theabovementioned related art (e.g., 60 operations). In this case, however,the size of the search space in each of the PDCCH region, the R-PDCCHregion in slot 0, and the R-PDCCH region in slot 1 becomes approximately1/3, and thus the possibility that the base station becomes unable toallocate CCEs to DCI for a specific terminal (i.e., a blockingprobability) may increase. In other words, it may lead to a drop insystem throughput as a result of not being able to use resourcesefficiently. Accordingly, a method is desired where downlink allocationcontrol information intended for a terminal under the control of thebase station is efficiently transmitted using a resource region providedfor downlink allocation control information intended for a relaystation.

The claimed invention is made in view of the points above, and an objectthereof is to provide a base station, a terminal, a transmission method,and a reception method that are capable of efficiently transmittingdownlink allocation control information.

Solution to Problem

A base station according to one aspect of the claimed inventioncomprises: a configuration section that configures a search space basedon a search space configuration rule corresponding to a slot to beconfigured, the search space being defined by a plurality of unit regioncandidates targeted for decoding at a terminal, each of the unit regioncandidates targeted for decoding being formed by one control channelelement or a plurality of concatenated control channel elements; and atransmitting section that disposes DCI in any of the plurality of unitregion candidates targeted for decoding included in the configuredsearch space and transmits the DCI to the terminal, wherein in thesearch space configuration rule, a plurality of aggregation levels forthe control channel elements are associated with respective numbers ofunit region candidates targeted for decoding, and a first search spaceconfiguration rule used for a first slot and a second search spaceconfiguration rule used for a second slot have mutually differentpatterns regarding the numbers of unit region candidates targeted fordecoding corresponding to the plurality of aggregation levels for thecontrol channel elements.

A terminal according to one aspect of the claimed invention comprises: afirst receiving section that configures a search space based on a searchspace configuration rule and performs blind decoding on each of aplurality of unit region candidates targeted for decoding forming thesearch space, each of the unit region candidates targeted for decodingbeing formed by one control channel element or a plurality ofconcatenated control channel elements; and a second receiving sectionthat receives a downlink data signal based on DCI intended for theterminal and disposed in any of the plurality of unit region candidatestargeted for decoding, wherein in the search space configuration rule, aplurality of aggregation levels for the control channel elements arerespectively associated with numbers of unit region candidates targetedfor decoding, and a first search space configuration rule used for afirst slot and a second search space configuration rule used for asecond slot have mutually different patterns regarding the numbers ofunit region candidates targeted for decoding corresponding to theplurality of aggregation levels for the control channel elements.

A transmission method according to one aspect of the claimed inventioncomprises the steps of: configuring a search space based on a searchspace configuration rule corresponding to a slot to be configured, thesearch space being defined by a plurality of unit region candidatestargeted for decoding at a terminal, each of the unit region candidatestargeted for decoding being formed by one control channel element or aplurality of concatenated control channel elements; and disposing DCI inany of the plurality of unit region candidates targeted for decodingincluded in the configured search space and transmitting the DCI to theterminal, wherein in the search space configuration rule, a plurality ofaggregation levels for the control channel elements are associated withrespective numbers of unit region candidates targeted for decoding; anda first search space configuration rule used for a first slot and asecond search space configuration rule used for a second slot havemutually different patterns regarding the numbers of unit regioncandidates targeted for decoding corresponding to the plurality ofaggregation levels for the control channel elements.

A reception method according to one aspect of the claimed inventioncomprises the steps of: configuring a search space based on a searchspace configuration rule and performing blind decoding on each of aplurality of unit region candidates targeted for decoding forming thesearch space, each of the unit region candidates targeted for decodingbeing formed by one control channel element or a plurality ofconcatenated control channel elements; and receiving a downlink datasignal based on DCI intended for oneself and disposed in any of theplurality of unit region candidates targeted for decoding, wherein inthe search space configuration rule, a plurality of aggregation levelsfor the control channel elements are respectively associated withnumbers of unit region candidates targeted for decoding; and a firstsearch space configuration rule used for a first slot and a secondsearch space configuration rule used for a second slot have mutuallydifferent patterns regarding the numbers of unit region candidatestargeted for decoding corresponding to the plurality of aggregationlevels for the control channel elements.

Advantageous Effects of Invention

With the claimed invention, it is possible to provide a base station, aterminal, a transmission method, and a reception method capable ofefficiently transmitting downlink allocation control information.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 illustrates an example PDCCH region;

FIG. 2 is a diagram for explaining search spaces;

FIG. 3 is a diagram for explaining search spaces;

FIG. 4 is a diagram for explaining a communication system including aradio communication relay apparatus;

FIG. 5 illustrates an example of R-PDCCH regions;

FIG. 6 is a diagram for explaining a mapping example of a PDCCH;

FIG. 7 is a principal block diagram of a base station according toEmbodiment 1 of the claimed invention;

FIG. 8 is a principal block diagram of a terminal according toEmbodiment 1 of the claimed invention;

FIG. 9 is a block diagram illustrating the configuration of the basestation according to Embodiment 1 of the claimed invention;

FIG. 10 is a block diagram illustrating the configuration of theterminal according to Embodiment 1 of the claimed invention;

FIG. 11 is a diagram illustrating variation 1 of a search spaceconfiguration rule;

FIG. 12 is a diagram illustrating a method of calculating an adequateR-CCE aggregation level;

FIG. 13 is a diagram showing examples of the number of REs forming oneR-CCE;

FIG. 14 is a diagram comparing slot 0 and slot 1 in terms of therelationship between the adequate number of REs and R-CCE aggregationlevel;

FIG. 15 is a diagram illustrating variation 2 of a search spaceconfiguration rule;

FIG. 16 is a diagram illustrating variation 3 of a search spaceconfiguration rule;

FIG. 17 is a diagram illustrating variation 4 of a search spaceconfiguration rule;

FIG. 18 is a diagram illustrating variation 5 of a search spaceconfiguration rule;

FIG. 19 is a diagram illustrating variation 6 of a search spaceconfiguration rule; and

FIG. 20 is a diagram illustrating variation 7 of a search spaceconfiguration rule.

DESCRIPTION OF EMBODIMENTS

Embodiments of the claimed invention are described in detail below withreference to the accompanying drawings. In the embodiments, the samereference numerals are used for denoting the same components, and aredundant description thereof is omitted.

Embodiment 1

(System Overview)

A communication system according to Embodiment 1 of the claimedinvention includes base station 100 and terminal 200. Base station 100is an LTE-A base station, and terminal 200 is an LTE-A terminal.

FIG. 7 is a principal block diagram of base station 100 according toEmbodiment 1 of the claimed invention. Search space configurationsection 103 of base station 100 configures, based on a search spaceconfiguration rule and per slot for each downlink control channel, asearch space defined by a plurality of unit region candidates targetedfor decoding in terminal 200. Allocating section 108 disposes DCI in anyof the unit region candidates targeted for decoding. Thus, the DCIdisposed in the unit region candidate targeted for decoding istransmitted to terminal 200.

FIG. 8 is a principal block diagram of terminal 200 according toEmbodiment 1 of the claimed invention. In terminal 200, PDCCH receivingsection 207 configures a search space based on a search spaceconfiguration rule, and performs blind decoding on each of a pluralityof unit region candidates targeted for decoding forming the searchspace. PDSCH receiving section 208 receives downlink data signals on thebasis of the DCI disposed in any one of the unit region candidatestargeted for decoding and directed to the device.

(Configuration of Base Station 100)

FIG. 9 is a block diagram illustrating a configuration of base station100 according to Embodiment 1 of the claimed invention. In FIG. 9, basestation 100 includes configuration section 101, control section 102,search space configuration section 103, PDCCH generating section 104,coding/modulating sections 105, 106 and 107, allocating section 108,multiplexing section 109, inverse fast Fourier transform (IFFT) section110, cyclic prefix (CP) adding section 111, RF transmitting section 112,antenna 113, RF receiving section 114, CP removing section 115, fastFourier transform (FFT) section 116, extracting section 117, inversediscrete Fourier transform (IDFT) section 118, data receiving section119, and ACK/NACK receiving section 120.

Configuration section 101 configures a resource region for use in thetransmission of DCI to terminal 200 and also configures eachtransmission mode for uplink and downlink for terminal 200. Theconfiguring of a resource region and the configuring of a transmissionmode are performed for each terminal 200 to be configured. Configurationinformation about a resource region and a transmission mode is sent tocontrol section 102, search space configuration section 103, PDCCHgenerating section 104, and coding/modulating section 106.

Specifically, configuration section 101 includes transmission regionconfiguration section 131 and transmission mode configuration section132.

Transmission region configuration section 131 configures a resourceregion for use in the transmission of DCI to terminal 200. Candidatesfor the resource regions to be configured include a PDCCH region, anR-PDCCH region in slot 0, and an R-PDCCH region in slot 1. For example,normally, a PDCCH region is configured for terminal 200, and a largenumber of terminals 200 communicate under the control of base station100. Accordingly, if the allocation of PDCCH region is expected to betight or if it is determined that significant interference occurs in thePDCCH region, then an R-PDCCH region in slot 0 or an R-PDCCH region inslot 1 is configured for terminal 200.

Transmission mode configuration section 132 configures the transmissionmode (for example, spatial multiplexing MIMO transmission, beamformingtransmission, and non-consecutive band allocation) of each of uplink anddownlink for terminal 200.

Configuration information about a resource region and a transmissionmode is reported to each terminal 200 via coding/modulating section 106as upper-layer control information (RRC control information or RRCsignaling).

Control section 102 generates allocation control information includingMCS information, resource (i.e., RB) allocation information, and a newdata indicator (NDI). As the resource allocation information, controlsection 102 generates uplink resource allocation information indicatingan uplink resource (for example, a Physical Uplink Shared Channel(PUSCH)) to which uplink data from terminal 200 is allocated, ordownlink resource allocation information indicating a downlink resource(for example, a Physical Downlink Shared Channel (PDSCH)) to whichdownlink data to terminal 200 is allocated.

Furthermore, on the basis of configuration information received fromconfiguration section 101, control section 102 generates, for eachterminal 200, allocation control information (any one of DCI 0A and DCI0B) based on a transmission mode of the uplink for terminal 200,allocation control information (any one of DCI 1, DCI 1B, DCI 1D, DCI 2,and DCI 2A) based on a transmission mode of the downlink, or allocationcontrol information (DCI 0/1A) common to all the terminals.

For example, in order to improve throughput during normal datatransmission, control section 102 generates allocation controlinformation (any one of DCI 1, DCI 1B, DCI 1D, DCI 2, DCI 2A, DCI 0A,and DCI 0B) corresponding to the transmission mode of each terminal 200so as to allow data transmission in the transmission mode configured foreach terminal 200. As a result, data can be transmitted in thetransmission mode configured for each terminal 200, which improvesthroughput.

However, an abrupt change in the condition of a propagation path or achange in interference from an adjacent cell may cause frequent errorsin receiving data with the transmission mode configured for eachterminal 200. In this case, control section 102 generates allocationcontrol information in the format (DCI 0/1A) common to all the terminalsand transmits data in a robust default transmission mode. As a result,robust data transmission is allowed even if a propagation environment isabruptly changed.

Also, when upper-layer control information (i.e., RRC signaling) istransmitted for the notification of a transmission mode change underdeteriorated conditions of a propagation path, control section 102generates allocation control information (i.e., DCI 0/1A) common to allthe terminals and transmits the information using the defaulttransmission mode. The number of information bits of DCI 0/1A common toall the terminals is smaller than those of DCI 1, DCI 2, DCI 2A, DCI 0A,and DCI 0B which are dependent on the transmission mode. For thisreason, if the same number of CCEs is set, DCI 0/1A can allowtransmission at a lower coding rate than that related to DCI 1, DCI 2,DCI 2A, DCI 0A, and DCI 0B. Thus, use of DCI 0/1A in control section 102under a deteriorated condition of a propagation path enables a terminalhaving a poor condition of a propagation path to receive allocationcontrol information (and data) with a low error rate.

Control section 102 also generates allocation control information for ashared channel (for example, DCI 1C and 1A) for the allocation of datacommon to a plurality of terminals, such as broadcast and paginginformation, in addition to the allocation control information for theallocation of terminal-specific data.

From among the generated allocation control information for theallocation of terminal-specific data, control section 102 outputs MCSinformation and an NDI to PDCCH generating section 104, uplink resourceallocation information to PDCCH generating section 104 and extractingsection 117, and downlink resource allocation information to PDCCHgenerating section 104 and multiplexing section 109. Control section 102also outputs the generated allocation control information for a sharedchannel to PDCCH generating section 104.

Search space configuration section 103 configures a search space basedon the search space configuration rule associated with the configuredresource region indicated by configuration information received fromconfiguration section 101. Each search space configuration rule isstored as a table in memory included in search space configurationsection 103. A search space includes a common search space (C-SS) and aunique search space (UE-SS) as described above. The common search space(C-SS) is a search space common to all the terminals, and the uniquesearch space (UE-SS) is a search space specific to each terminal asdescribed above.

Specifically, search space configuration section 103 configurespreconfigured CCEs (for example, 16 CCEs′-worth of CCEs from the firstCCE) as a C-SS. A CCE is a basic unit.

Search space configuration section 103 also configures a UE-SS for eachterminal. For example, search space configuration section 103 determinesa UE-SS for a certain terminal on the basis of the ID of the terminal, aCCE number obtained by calculations using a hash function forrandomization, and the number of CCEs (L) that form a search space.

If a resource region configured by configuration section 101 is a PDCCHregion, search space configuration section 103 configures a search spaceas shown in FIG. 2, for example. In other words, a pattern of the numberof DCI allocation region candidates with respect to the CCE aggregationlevel in the search spaces shown in FIG. 2 is a search spaceconfiguration rule for when a resource region configured byconfiguration section 101 is a PDCCH region.

In FIG. 2, with respect to CCE aggregation level 4 for the PDCCH, fourDCI allocation region candidates (i.e., CCEs 0 to 3, CCEs 4 to 7, CCEs 8to 11, and CCEs 12 to 15) are configured as a C-SS. Also, with respectto CCE aggregation level 8 for the PDCCH, two DCI allocation regioncandidates (i.e., CCEs 0 to 7 and CCEs 8 to 15) are configured as aC-SS. In other words, in FIG. 2, a total of six DCI allocation regioncandidates are configured as C-SSs.

Furthermore, in FIG. 2, with respect to CCE aggregation level 1, six DCIallocation region candidates (i.e., each of CCEs 16 to 21) areconfigured as a UE-SS. With respect to CCE aggregation level 2, six DCIallocation region candidates (i.e., CCEs 6 to 17 divided into units oftwo each) are configured as a UE-SS. With respect to CCE aggregationlevel 4, two DCI allocation region candidates (i.e., CCEs 20 to 23 andCCEs 24 to 27) are configured as a UE-SS. With respect to CCEaggregation level 8, two DCI allocation region candidates (i.e., CCEs 16to 23 and CCEs 24 to 31) are configured as a UE-SS. In other words, inFIG. 2, a total of sixteen DCI allocation region candidates areconfigured as UE-SSs.

Also, if the resource region configured by configuration section 101 isan R-PDCCH region in slot 0 or an R-PDCCH region in slot 1, searchspaces are configured in accordance with a search space configurationrule corresponding to each. The search space configuration rule for theR-PDCCH region in slot 0 and the search space configuration rule for theR-PDCCH region in slot 1 will be described in detail, hereinafter.

PDCCH generating section 104 generates DCI including allocation controlinformation received from control section 102 for the allocation ofterminal-specific data (i.e., uplink resource allocation information,downlink resource allocation information, MCS information, an NDI,and/or the like for each terminal) or DCI including allocation controlinformation for a shared channel (i.e., broadcast information, paginginformation, and other information common to terminals). In so doing,PDCCH generating section 104 adds CRC bits to the uplink allocationcontrol information and the downlink allocation control informationgenerated for each terminal and masks (or scrambles) the CRC bits with aterminal ID. PDCCH generating section 104 then outputs the maskedsignals to coding/modulating section 105.

Coding/modulating section 105 modulates the DCI received from PDCCHgenerating section 104 after channel coding and outputs the modulatedsignals to allocating section 108. Coding/modulating section 105determines a coding rate set on the basis of channel quality indicator(CQI) information reported from each terminal so as to achieve asufficient reception quality in each terminal. For example, as adistance between a terminal and a cell boundary decreases (i.e., as thechannel quality of a terminal deteriorates), the coding rate to be setby coding/modulating section 105 decreases.

Allocating section 108 receives, from coding/modulating section 105, DCIincluding allocation control information for a shared channel and DCIincluding allocation control information for the allocation ofterminal-specific data to each terminal. Then, allocating section 108allocates the received DCI to each of CCEs or R-CCEs in a C-SS, or CCEsor R-CCEs in a UE-SS for each terminal in accordance with search spaceinformation received from search space configuration section 103.

For example, allocating section 108 selects one DCI allocation regioncandidate from a group of DCI allocation region candidates in a C-SS(for example, see FIG. 2). Allocating section 108 then allocates DCIincluding allocation control information for a shared channel to a CCE(or an R-CCE; hereinafter, sometimes simply referred to as “CCE” withoutdistinguishing “CCE” from “R-CCE”) in the selected DCI allocation regioncandidate.

In the case of a DCI format specific to the terminal (for example, DCI1, DCI 1B, DCI 1D, DCI 2, DCI 2A, DCI 0A, or DCI 0B), allocating section108 allocates a CCE in a UE-SS configured for the terminal to the DCI.On the other hand, if the DCI format intended for the terminal is a DCIformat common to all the terminals (for example, DCI 0/1A), allocatingsection 108 allocates a CCE in a C-SS or a CCE in a UE-SS configured forthe terminal to the DCI.

The CCE aggregation level to be allocated to one DCI item depends on thecoding rate and the number of DCI bits (namely, the amount of allocationcontrol information). For example, because the coding rate of DCIintended for a terminal located around a cell boundary is set low, morephysical resources are required. Accordingly, allocating section 108allocates more CCEs to DCI for a terminal located around a cellboundary.

Allocating section 108 then outputs information about the CCEs allocatedto the DCI to multiplexing section 109 and ACK/NACK receiving section120. Allocating section 108 outputs the coded/modulated DCI tomultiplexing section 109.

Coding/modulating section 106 modulates the configuration informationreceived from configuration section 101 after channel coding and outputsthe modulated configuration information to multiplexing section 109.

Coding/modulating section 107 modulates the input transmission data(downlink data) after channel coding and outputs the modulatedtransmission data signals to multiplexing section 109.

Multiplexing section 109 multiplexes the coded/modulated DCI signalreceived from allocating section 108, the configuration informationreceived from coding/modulating section 106, and the data signals(namely, PDSCH signals) input from coding/modulating section 107 in thetime domain and the frequency domain. Multiplexing section 109 maps thePDCCH signals and the data signals (PDSCH signals) on the basis of thedownlink resource allocation information received from control section102. Multiplexing section 109 may also map the configuration informationonto the PDSCH. Multiplexing section 109 then outputs the multiplexedsignals to IFFT section 110.

IFFT section 110 converts the multiplexed signals from multiplexingsection 109 for each antenna into a time waveform. CP adding section 111adds a CP to the time waveform to obtain OFDM signals.

RF transmitting section 112 performs radio processing for transmission(for example, up-conversion or digital-analog (D/A) conversion) on theOFDM signals input from CP adding section 111 and transmits theresultant signals via antenna 113.

RF receiving section 114 also performs radio processing for reception(for example, down-conversion or analog-digital (A/D) conversion) onradio signals received via antenna 113 at a receiving band and outputsthe resultant received signals to CP removing section 115.

CP removing section 115 removes the CP from the received signals andfast Fourier transform (FFT) section 116 converts the received signalsfrom which the CP is removed into frequency domain signals.

Extracting section 117 extracts uplink data from the frequency domainsignals received from FFT section 116 on the basis of uplink resourceallocation information received from control section 102. IDFT section118 converts the extracted signals into time domain signals and outputsthe time domain signals to data receiving section 119 and ACK/NACKreceiving section 120.

Data receiving section 119 decodes the time domain signals input fromIDFT section 118. Data receiving section 119 then outputs decoded uplinkdata as received data.

ACK/NACK receiving section 120 extracts, from the time domain signalsreceived from IDFT section 118, ACK/NACK signals from each terminal forthe downlink data (PDSCH signals). Specifically, ACK/NACK receivingsection 120 extracts the ACK/NACK signals from an uplink control channel(e.g., a Physical Uplink Control Channel (PUCCH) on the basis of theinformation received from allocating section 108. The uplink controlchannel is associated with the CCEs used for the transmission of thedownlink allocation control information corresponding to the downlinkdata.

ACK/NACK receiving section 120 then determines the ACK or NACK of theextracted ACK/NACK signals.

One reason that the CCEs and the PUCCH are associated with each other isto obviate the need for signaling sent by the base station to notifyeach terminal of a PUCCH for use in transmitting ACK/NACK signals fromthe terminal, which thereby allows downlink communication resources tobe used efficiently. Consequently, in accordance with this association,each terminal determines a PUCCH for use in transmitting ACK/NACKsignals on the basis of the CCEs to which downlink allocation controlinformation (DCI) for the terminal is mapped.

(Configuration of Terminal 200)

FIG. 10 is a block diagram illustrating the configuration of terminal200 according to Embodiment 1 of the claimed invention. Terminal 200 isan LTE-A terminal, receives data signals (i.e., downlink data) through aplurality of downlink unit carriers, and transmits ACK/NACK signals forthe data signals to base station 100 via a PUCCH for one uplink unitcarrier.

In FIG. 10, terminal 200 includes antenna 201, RF receiving section 202,CP removing section 203, FFT section 204, demultiplexing section 205,configuration information receiving section 206, PDCCH receiving section207, PDSCH receiving section 208, modulating sections 209 and 210, DFTsection 211, mapping section 212, IFFT section 213, CP adding section214, and RF transmitting section 215.

RF receiving section 202 sets a reception band on the basis of bandinformation received from configuration information receiving section206. RF receiving section 202 performs radio processing for reception(e.g., down-conversion or analog-digital (A/D) conversion) on radiosignals (OFDM signals in this case) received via antenna 201 in thereception band and outputs the resultant received signals to CP removingsection 203. The received signals may include a PDSCH signal, DCI, andupper layer control information including configuration information. TheDCI (allocation control information) is allocated to a common searchspace (C-SS) configured for terminal 200 and other terminals or to aunique search space (UE-SS) configured for terminal 200.

CP removing section 203 removes a CP from the received signals and FFTsection 204 converts the received signals from which the CP is removedinto frequency domain signals. The frequency domain signals are outputto demultiplexing section 205.

Demultiplexing section 205 outputs to PDCCH receiving section 207, fromsignals received from FFT section 204, a component that may include DCI(i.e., signals extracted from a PDCCH region and an R-PDCCH region).Demultiplexing section 205 also outputs upper layer control signals(e.g., RRC signaling) including configuration information toconfiguration information receiving section 206 and data signals (i.e.,PDSCH signals) to PDSCH receiving section 208. If the upper layercontrol signals including the configuration information are transmittedthrough a PDSCH, demultiplexing section 205 extracts the configurationinformation from the signals received by PDSCH receiving section 208.

Configuration information receiving section 206 reads the followinginformation from the upper layer control signals received fromdemultiplexing section 205. In other words, the information to be readincludes: information indicating uplink and downlink unit carriers setfor the terminal, information indicating a terminal ID set for theterminal, information indicating a resource region configured for theterminal for use in transmitting DCI, information indicating a referencesignal set for the terminal, and information indicating a transmissionmode configured for the terminal.

The information indicating uplink and downlink unit carriers set for theterminal is output to PDCCH receiving section 207, RF receiving section202 and RF transmitting section 215 as band information. The informationindicating a terminal ID set for the terminal is output to PDCCHreceiving section 207 as terminal ID information. The informationindicating a resource region for use in transmitting DCI is output toPDCCH receiving section 207 as search space region information. Theinformation indicating a reference signal set for the terminal is outputto PDCCH receiving section 207 as reference signal information. Theinformation indicating a transmission mode configured for the terminalis output to PDCCH receiving section 207 as transmission modeinformation.

PDCCH receiving section 207 blind-decodes (monitors) the signals inputfrom demultiplexing section 205 to obtain DCI for the terminal. Theblind decoding is performed on unit region candidates targeted fordecoding, specified in the search space configuration rule associatedwith a resource region configured for the terminal. Each search spaceconfiguration rule is saved as a table in memory included in PDCCHreceiving section 207. PDCCH receiving section 207 performsblind-decoding for a DCI format for the allocation of data common to allthe terminals (for example, DCI 0/1A), a DCI format dependent on thetransmission mode configured for the terminal (for example, DCI 1, DCI2, DCI 2A, DCI 0A, and DCI 0B), and a DCI format for the allocation of ashared channel common to all the terminals (for example, DCI 1C and DCI1A). This operation creates DCI including allocation control informationon the DCI formats.

If a region indicated by search space region information received fromconfiguration information receiving section 206 is a PDCCH region, PDCCHreceiving section 207 performs, with respect to a C-SS, blind-decodingfor the DCI formats for shared channel allocation (DCI 1C and DCI 1A)and the DCI format for the allocation of data common to all theterminals (DCI 0/1A) on the basis of the search space configuration rulefor when the resource region is a PDCCH region. Specifically, for eachunit region candidate targeted for decoding in a C-SS (i.e., candidatesof a CCE region allocated to terminal 200), PDCCH receiving section 207performs demodulation and decoding based on the size of the DCI formatfor shared channel allocation and the size of the DCI format for theallocation of data common to all the terminals. For the decoded signals,PDCCH receiving section 207 demasks CRC bits with an ID common to aplurality of terminals. PDCCH receiving section 207 then determinessignals for which “CRC=OK” (i.e. no error) is returned as a result ofthe demasking to be DCI including allocation control information for ashared channel. For the decoded signals, PDCCH receiving section 207further demasks the CRC bits with the ID of the terminal indicated bythe terminal ID information. PDCCH receiving section 207 then determinessignals for which “CRC=OK” (i.e. no error) is returned as a result ofthe demasking to be DCI including allocation control information for theterminal. In other words, in a C-SS, PDCCH receiving section 207determines by means of a terminal ID (i.e., an ID common to a pluralityof terminals or the ID of terminal 200) whether allocation controlinformation of DCI 0/1A is for a shared channel or for the allocation ofdata to the terminal.

PDCCH receiving section 207 calculates a UE-SS for the terminal for CCEaggregation level with the terminal ID indicated by the terminal IDinformation received from configuration information receiving section206. For each blind decoding region candidate in the obtained UE-SS,PDCCH receiving section 207 then performs demodulation and decodingbased on the size of the DCI format corresponding to the transmissionmode configured for the terminal (the transmission mode indicated by thetransmission mode information) and the size of the DCI format common toall the terminals (DCI 0/1A). For the decoded signals, PDCCH receivingsection 207 demasks CRC bits with the ID of the terminal. PDCCHreceiving section 207 determines signals for which “CRC=OK” (i.e. noerror) is returned as a result of demasking to be DCI for the terminal.

Even if the region indicated by the search space region informationreceived from configuration information receiving section 206 is anR-PDCCH region in slot 0 or an R-PDCCH region in slot 1, PDCCH receivingsection 207 also performs blind decoding on the basis of the searchspace configuration rule corresponding to each region. The search spaceconfiguration rule for an R-PDCCH region in slot 0 and the search spaceconfiguration rule for an R-PDCCH region in slot 1 will be described indetail hereinafter. If no search space region information (i.e., searchspace allocation) is received from configuration information receivingsection 206 (i.e., if base station 100 transmits no search space regioninformation), terminal 200 may perform blind decoding withoutconsidering the allocation of search spaces.

Upon reception of downlink allocation control information, PDCCHreceiving section 207 outputs downlink resource allocation informationin the DCI for the terminal to PDSCH receiving section 208. Uponreception of uplink allocation control information, PDCCH receivingsection 207 outputs uplink resource allocation information to mappingsection 212. PDCCH receiving section 207 also outputs the CCE number forthe CCE used for the transmission of the DCI for the terminal (i.e., CCEused for the transmission of the signals for which “CRC=OK”) to mappingsection 212 (CCE number for the leading CCE if the CCE aggregation levelis plural). The details of blind decoding (monitoring) in the PDCCHreceiving section will be described hereinafter.

PDSCH receiving section 208 extracts received data (i.e., downlink data)from the PDSCH signals from demultiplexing section 205 on the basis ofthe downlink resource allocation information received from PDCCHreceiving section 207. PDSCH receiving section 208 also detects anyerror in the extracted received data (i.e., downlink data). If an erroris found in the received data as a result of the error detection, PDSCHreceiving section 208 generates NACK signals as ACK/NACK signals. If noerror is found in the received data, PDSCH receiving section 208generates ACK signals as ACK/NACK signals. The ACK/NACK signals areoutput to modulating section 209.

Modulating section 209 modulates the ACK/NACK signals received fromPDSCH receiving section 208 and outputs the modulated ACK/NACK signalsto mapping section 212.

Modulating section 210 modulates transmission data (i.e., uplink data)and outputs the modulated data signal to DFT section 211.

DFT section 211 converts the data signals received from modulatingsection 210 into the frequency domain and outputs a plurality ofresultant frequency components to mapping section 212.

Mapping section 212 maps the frequency components received from DFTsection 211 to a PUSCH included in the uplink unit carrier in accordancewith the uplink resource allocation information received from PDCCHreceiving section 207. Mapping section 212 also identifies a PUCCH inaccordance with the CCE number received from PDCCH receiving section207. Mapping section 212 then maps the ACK/NACK signals input frommodulating section 209 to the identified PUCCH.

IFFT section 213 converts the plurality of frequency components mappedto the PUSCH into a time domain waveform. CP adding section 214 adds aCP to the time domain waveform.

RF transmitting section 215 can vary the transmission band. RFtransmitting section 215 determines a specific transmission band on thebasis of the band information received from configuration informationreceiving section 206. RF transmitting section 215 then performstransmission radio processing (for example, up-conversion ordigital-analog (D/A) conversion) on the CP-added signals and transmitsthe resultant signals via antenna 201.

(Operations of Base Station 100 and Terminal 200)

Configuration section 101 of base station 100 configures a resourceregion used for the transmission of DCI for terminal 200. Candidates ofthe resource region to be configured include a PDCCH region, an R-PDCCHregion in slot 0, and an R-PDCCH region in slot 1.

Search space configuration section 103 configures a search space on thebasis of the search space configuration rule associated with theconfigured resource region indicated by configuration informationreceived from configuration section 101. A “first search spaceconfiguration rule” that is used when the resource region is an R-PDCCHregion in slot 0 and a “second search space configuration rule” that isused when the resource region is an R-PDCCH region in slot 1 havemutually different patterns regarding the number of unit regioncandidates targeted for decoding with respect to CCE aggregation level.In other words, for the R-PDCCH region in slot 0 and the R-PDCCH regionin slot 1, patterns regarding the number of unit region candidatestargeted for decoding with respect to CCE aggregation level are definedindependently.

Variations of the “first search space configuration rule” and the“second search space configuration rule” are described below.

<Variation 1 of Search Space Configuration Rule>

FIG. 11 is a diagram illustrating variation 1 of a search spaceconfiguration rule. As shown in FIG. 11, the pattern of the first searchspace configuration rule is a pattern where the numbers of unit regioncandidates targeted for decoding are 0, 6, 4, and 2 for CCE aggregationlevels 1, 2, 4, and 8, respectively. On the other hand, the pattern ofthe second search space configuration rule is a pattern where thenumbers of unit region candidates targeted for decoding are 6, 4, 2, and0 for CCE aggregation levels 1, 2, 4, and 8, respectively.

As shown in FIG. 12, base station 100 determines an adequate MCS (i.e.,an adequate coding rate) so as to adequately achieve the desiredcommunication quality (for example, in LTE, “BLER=1% or less” isspecified for a PDCCH) with the number of DCI bits to be transmitted toterminal 200 being based on actual communication quality (for example,SINR=*dB). Based on the number of DCI bits and the adequate coding rate,base station 100 then calculates what number of REs would be adequateand also calculates an adequate R-CCE aggregation level based on thenumber of REs per R-CCE, which varies for each slot or for eachreference signal location. The modulation scheme of R-PDCCH is QPSK.

As shown in FIG. 13, the number of REs forming one R-CCE differs betweenslot 0 and slot 1. In FIG. 13, those marked “*1” correspond to 3GPPTS36.211 V9.1.0, and those marked “*2” correspond to 3GPP TS36.814V9.0.0. Specifically, the number of REs forming an R-CCE of R-PDCCH inslot 0 is less than the number of REs forming an R-CCE of R-PDCCH inslot 1.

Accordingly, as shown in FIG. 14, in order to obtain an adequate numberof REs, the R-CCE aggregation level would have to be made relativelygreater for slot 0, which has a smaller number of REs per R-CCE, ascompared to slot 1, which has a greater number of REs per R-CCE.

This requirement is met by variation 1 of the search space configurationrule mentioned above. In other words, in variation 1 of the search spaceconfiguration rule, the patterns of the first search space configurationrule and the second search space configuration rule are determined inaccordance with the number of REs per R-CCE. The peak position (i.e.,the center of weight) of the distribution of unit region candidategroups targeted for decoding contained in the search space with respectto R-CCE aggregation level is located towards greater R-CCE aggregationlevels for the pattern of the first search space configuration rule thanit is for the pattern of the second search space configuration rule.

The fact that “for the pattern of the first search space configurationrule, the peak position of the distribution of unit region candidategroups targeted for decoding with respect to R-CCE aggregation level isshifted towards greater CCE aggregation levels than it is for thepattern of the second search space configuration rule” signifies thematters below.

<Matter 1> It signifies that the weighted average of the number of REsper R-CCE aggregation level with respect to the number of blind decodingoperations is greater for the first search space configuration rule thanit is for the second search space configuration rule. A number isrepresented by ‘#’ in the following equations. The weighted average ofthe number REs per R-CCE aggregation level with respect to the number ofblind decoding operations (i.e., the number of unit region candidatestargeted for decoding) is represented by Equation (1) below:

$\begin{matrix}{\left\lbrack {{Eq}.\mspace{14mu} 1} \right\rbrack\mspace{664mu}} & \; \\{X_{{Slot}\# n} = \frac{\begin{matrix}{\sum\limits_{R\text{-}{CCEaggregation}\mspace{14mu}{level}}^{\;}\left( {\left( {\#\mspace{14mu}{of}\mspace{14mu}{REs}\mspace{14mu}{per}\mspace{14mu} R\text{-}{CCE}\mspace{14mu}{{agg}.\mspace{14mu}{level}}} \right) \times} \right.} \\\left. \left( {\#\mspace{14mu}{of}\mspace{14mu}{blind}\mspace{14mu}{decoding}\mspace{14mu}{operations}} \right) \right)\end{matrix}}{\sum\limits_{R\text{-}{CCEaggregation}\mspace{14mu}{level}}^{\;}\left( {\#\mspace{14mu}{of}\mspace{14mu}{blind}\mspace{14mu}{decoding}\mspace{14mu}{operations}} \right)}} & (1)\end{matrix}$

Equation (1) may be modified as in Equation (2) below.

$\begin{matrix}\left\lbrack {{Eq}.\mspace{14mu} 2} \right\rbrack & \; \\\begin{matrix}{X_{{Slot}\# n} = \frac{\begin{matrix}{\sum\limits_{R\text{-}{CCEaggregation}\mspace{14mu}{level}}^{\;}\left( {\left( {\#\mspace{14mu}{of}\mspace{14mu}{REs}\mspace{14mu}{per}\mspace{14mu} R\text{-}{CCE}\mspace{14mu}{{agg}.\mspace{14mu}{level}}} \right) \times} \right.} \\\left. \left( {\#\mspace{14mu}{of}\mspace{14mu}{blind}\mspace{14mu}{decoding}\mspace{14mu}{operations}} \right) \right)\end{matrix}}{\sum\limits_{R\text{-}{CCEaggregation}\mspace{14mu}{level}}^{\;}\left( {\#\mspace{14mu}{of}\mspace{14mu}{blind}\mspace{14mu}{decoding}\mspace{14mu}{operations}} \right)}} \\{= {\left( {\#\mspace{14mu}{of}\mspace{14mu}{REs}\mspace{14mu}{per}\mspace{14mu} R\text{-}{CCE}} \right) \cdot}} \\{\frac{\begin{matrix}{\sum\limits_{R\text{-}{CCEaggregation}\mspace{14mu}{level}}^{\;}\left( {\left( {R\text{-}{CCE}\mspace{14mu}{{agg}.\mspace{14mu}{level}}} \right) \times} \right.} \\\left. \left( {\#\mspace{14mu}{of}\mspace{14mu}{blind}\mspace{14mu}{decoding}\mspace{14mu}{operations}} \right) \right)\end{matrix}}{\sum\limits_{R\text{-}{CCEaggregation}\mspace{14mu}{level}}^{\;}\left( {\#\mspace{14mu}{of}\mspace{14mu}{blind}\mspace{14mu}{decoding}\mspace{14mu}{operations}} \right)}} \\{= {\left( {\#\mspace{14mu}{of}\mspace{14mu}{REs}\mspace{14mu}{per}\mspace{14mu} R\text{-}{CCE}} \right) \cdot}} \\{\left( {{weighted}\mspace{14mu}{{avg}.\mspace{14mu}{of}}\mspace{14mu} R\text{-}{CCE}\mspace{14mu}{{agg}.\mspace{14mu}{levels}}\mspace{14mu}{with}\mspace{14mu}{respect}\mspace{14mu}{to}} \right.} \\{\left. {\#\mspace{14mu}{of}\mspace{14mu}{blind}\mspace{14mu}{decoding}\mspace{14mu}{operations}} \right)\;}\end{matrix} & (2)\end{matrix}$

Accordingly, the weighted average of the number of REs per R-CCEaggregation level with respect to the number of blind decodingoperations may also be described as the product obtained by multiplyingthe number of REs per R-CCE with the weighted average of R-CCEaggregation levels with respect to the number of blind decodingoperations.

<Matter 2> It signifies that the R-CCE aggregation level at which thenumber of unit region candidates targeted for decoding is greatest forthe first search space configuration rule is greater than it is for thesecond search space configuration rule. If there are a plurality ofR-CCE aggregation levels at which the number of unit region candidatestargeted for decoding is greatest, it signifies that the average valueof the R-CCE aggregation levels at which the number of unit regioncandidates targeted for decoding is greatest is greater for the firstsearch space configuration rule than it is for the second search spaceconfiguration rule.

<Matter 3> It signifies that the weighted average of R-CCE aggregationlevels with respect to the number of blind decoding operations isgreater for the first search space configuration rule than it is for thesecond search space configuration rule.

<Matter 4> It signifies that the weighted average of R-CCE aggregationlevel indices with respect to the number of blind decoding operations isgreater for the first search space configuration rule than it is for thesecond search space configuration rule. R-CCE aggregation level indicesare numbered 0, 1, 2, 3 in ascending order of R-CCE aggregation level.With respect to R-CCE aggregation levels 1, 2, 4, and 8, their R-CCEaggregation level indices are defined as 0, 1, 2, and 3, respectively.

Assuming that the number of REs per R-CCE is 44 in slot 0 and 72 in slot1, whether or not the above-mentioned <Matter 1> to <Matter 4> aresatisfied may specifically be confirmed as follows.

<Matter 1>

The weighted average of the number of REs per R-CCE aggregation levelwith respect to the number of blind decoding operations is(44×0+88×6+176×4+352×2)/(0+6+4+2)≈161 for the first search spaceconfiguration rule, and (72×6+144×4+288×2+576×0)/(6+4+2+0)=132 for thesecond search space configuration rule. Thus, the relationship “firstsearch space configuration rule>second search space configuration rule”is satisfied.

<Matter 2>

The R-CCE aggregation level at which the number of blind decodingoperations becomes greatest is 2 for the first search spaceconfiguration rule, and 1 for the second search space configurationrule. Thus, the relationship “first search space configurationrule>second search space configuration rule” is satisfied.

<Matter 3>

The weighted average of R-CCE aggregation levels with respect to thenumber of blind decoding operations is (1×0+2×6+4×4+8×2)/(0+6+4+2)≈3.67for the first search space configuration rule, and(1×6+2×4+4×2+8×0)/(6+4+2+0)≈1.83 for the second search spaceconfiguration rule. Thus, the relationship “first search spaceconfiguration rule>second search space configuration rule” is satisfied.

<Matter 4>

The weighted average of R-CCE aggregation level indices with respect tothe number of blind decoding operations is(0×0+1×6+2×4+3×2)/(0+6+4+2)≈1.67 for the first search spaceconfiguration rule, and (0×6+1×4+2×2+3×0)/(6+4+2+0)≈0.67 for the secondsearch space configuration rule. Thus, the relationship “first searchspace configuration rule>second search space configuration rule” issatisfied.

In expanding the PDCCH region to the R-PDCCH region as well, if one wereto simply expand it, the number of blind decoding operations in terminal200 would increase, consequently causing the circuit size of terminal200 to become bigger. If a search space as defined in LTE is configuredfor each of the PDCCH region, the R-PDCCH region in slot 0, and theR-PDCCH region in slot 1, the number of blind decoding operations interminal 200 could be as high as 180 times (=60 (PDCCH region)+60(R-PDCCH region in slot 0)+60 (R-PDCCH region in slot 1)).

On the other hand, if one were to simply reduce the number of unitregion candidates targeted for decoding, the probability that all areused by other terminals and relay stations would become higher, causingthe blocking probability to rise.

In contrast, by using variation 1 of the search space configurationrule, efficient DCI transmission using an adequate number of RE groupsfor satisfying the desired communication quality becomes possible. As aresult, it also becomes possible to prevent the blocking probabilityfrom becoming high. This effect is common to all the variationsdiscussed hereinafter.

Furthermore, in the example provided for variation 1 of the search spaceconfiguration rule, the number of unit region candidates targeted fordecoding is reduced compared to the search space in LTE. Thus, it ispossible to prevent the circuit size of terminal 200 from becominglarger. In other words, in each of the variations described below, byreducing the number of unit region candidates targeted for decoding ascompared to the search space in LTE, similar effects may be attained.

<Variation 2 of Search Space Configuration Rule>

FIG. 15 is a diagram illustrating variation 2 of the search spaceconfiguration rule. As shown in FIG. 15, the pattern of the first searchspace configuration rule is a pattern where, for CCE aggregation levels1, 2, 4, and 8, the numbers of unit region candidates targeted fordecoding are 6, 6, 2, and 2, respectively. In other words, here, by wayof example, the same pattern as that of the search space configurationrule used for the PDCCH region is employed. On the other hand, thepattern of the second search space configuration rule is a patternwhere, for CCE aggregation levels 1, 2, 4, and 8, the numbers of unitregion candidates targeted for decoding are 6, 2, 2, and 2 (or 0),respectively.

Considering FIG. 13 in terms of slot 1, the number of REs per R-CCE inslot 1 is approximately twice the number of REs per R-CCE in slot 0. Assuch, in variation 2, the pattern of the second search spaceconfiguration rule is formed by simply shifting the pattern of the firstsearch space configuration rule towards lesser R-CCE aggregation levels.In so doing, the number of unit region candidates targeted for decodingfor R-CCE aggregation level=8 of the second search space configurationrule may be the smallest number of unit region candidates targeted fordecoding prior to shifting (=2), or it may be that no unit regioncandidate targeted for decoding is allocated (i.e., number of unitregion candidates targeted for decoding=0).

<Variation 3 of Search Space Configuration Rule>

FIG. 16 is a diagram illustrating variation 3 of the search spaceconfiguration rule. As shown in FIG. 16, the pattern of the first searchspace configuration rule is a pattern where, for CCE aggregation levels1, 2, 4, and 8, the numbers of unit region candidates targeted fordecoding are 6, 6, 2, and 2, respectively. In other words, here, by wayof example, the same pattern as that of the search space configurationrule used for the PDCCH region is employed. On the other hand, thepattern of the second search space configuration rule is a patternwhere, for CCE aggregation levels 1, 2, 4, and 8, the numbers of unitregion candidates targeted for decoding are 8, 3, 3, and 2,respectively.

In other words, the pattern of the second search space configurationrule of variation 3 is formed by allocating to the pattern of the secondsearch space configuration rule of variation 2 the amount by which thenumber of unit region candidates targeted for decoding has decreasedbetween the first search space configuration rule and the second searchspace configuration rule of variation 2 (i.e., 4). Specifically, in FIG.16, in order to weight the R-CCE aggregation level with the greatestnumber of unit region candidates targeted for decoding, the amount bywhich the number of unit region candidates targeted for decoding hasdecreased is allocated to CCE aggregation levels 1, 2, 4, and 8according to the allocation pattern +2, +1, +1, +0.

If, for example, allocation is to be carried out evenly, the amount bywhich the number of unit region candidates targeted for decoding hasdecreased may be allocated to R-CCE aggregation levels 1, 2, 4, and 8according to the allocation pattern +1, +1, +1, +1, respectively.Alternatively, the weighting method may be altered so that the amount bywhich the number of unit region candidates targeted for decoding hasdecreased is allocated according to the allocation pattern +4, +0, +0,+0, for example.

<Variation 4 of Search Space Configuration Rule>

FIG. 17 is a diagram illustrating variation 4 of the search spaceconfiguration rule. As shown in FIG. 17, the pattern of the first searchspace configuration rule is a pattern where, for CCE aggregation levels1, 2, 4, and 8, the numbers of unit region candidates targeted fordecoding are 2 (or 0), 6, 6, and 2, respectively. On the other hand, thepattern of the second search space configuration rule is a patternwhere, for CCE aggregation levels 1, 2, 4, and 8, the numbers of unitregion candidates targeted for decoding are 6, 6, 2, and 2,respectively. In other words, here, by way of example, the same patternas that of the search space configuration rule used for the PDCCH regionis employed.

Considering FIG. 13 in terms of slot 0, the number of REs per R-CCE inslot 0 is approximately 1/2 of the number of REs per R-CCE in slot 1. Assuch, in variation 4, the pattern of the first search spaceconfiguration rule is formed by simply shifting the pattern of thesecond search space configuration rule towards greater R-CCE aggregationlevels. In so doing, the number of unit region candidates targeted fordecoding for R-CCE aggregation level=1 of the first search spaceconfiguration rule may be the smallest number of unit region candidatestargeted for decoding prior to shifting (=2), or it may be that no unitregion candidate targeted for decoding is allocated (i.e., number ofunit region candidates targeted for decoding=0).

<Variation 5 of Search Space Configuration Rule>

FIG. 18 is a diagram illustrating variation 5 of the search spaceconfiguration rule. As shown in FIG. 18, the pattern of the first searchspace configuration rule is a pattern where, for CCE aggregation levels1, 2, 4, and 8, the numbers of unit region candidates targeted fordecoding are 0, 7, 7, and 2, respectively. On the other hand, thepattern of the second search space configuration rule is a patternwhere, for CCE aggregation levels 1, 2, 4, and 8, the numbers of unitregion candidates targeted for decoding are 6, 6, 2, and 2,respectively. In other words, here, by way of example, the same patternas that of the search space configuration rule used for the PDCCH regionis employed.

In other words, the pattern of the first search space configuration ruleof variation 5 is formed by allocating to the pattern of the firstsearch space configuration rule of variation 4 the amount by which thenumber of unit region candidates targeted for decoding has decreasedbetween the first search space configuration rule and the second searchspace configuration rule of variation 4 (i.e., 2). Specifically, in FIG.18, in order to weight the R-CCE aggregation level with the greatestnumber of unit region candidates targeted for decoding, the amount bywhich the number of unit region candidates targeted for decoding hasdecreased is allocated to CCE aggregation levels 1, 2, 4, and 8according to the allocation pattern +0, +1, +1, +0.

Allocating section 108 allocates the DCI to unit region candidatestargeted for decoding indicated by the search space information fromsearch space configuration section 103. The DCI is thus transmitted toterminal 200.

In terminal 200, if the region indicated by the search space regioninformation received from configuration information receiving section206 is an R-PDCCH region in slot 0 or an R-PDCCH region in slot 1, PDCCHreceiving section 207 performs blind decoding on the basis of the searchspace configuration rule corresponding to each. These rules correspondto the above-described rules adopted in base station 100.

According to the present embodiment, search space configuration section103 of base station 100, as described above, configures a search spacebased on the search space configuration rule corresponding to theR-PDCCH region of the slot to be configured. Allocating section 108disposes DCI in any one of the plurality of unit region candidatestargeted for decoding contained in the configured search space. A searchspace is composed of a plurality of unit region candidates targeted fordecoding in terminal 200 and each unit region candidate targeted fordecoding is composed of one or more concatenated R-CCEs (control channelelements).

In a search space configuration rule, corresponding numbers of unitregion candidates targeted for decoding are respectively associated witha plurality of aggregation levels regarding CCEs. The first search spaceconfiguration rule for slot 0 and the second search space configurationrule for slot 1 have mutually different patterns regarding the numbersof unit region candidates targeted for decoding with respect to theplurality of aggregation levels regarding R-CCEs. In other words,patterns regarding the number of unit region candidates targeted fordecoding with respect to R-CCE aggregation level are independentlyspecified for the R-PDCCH region in slot 0 and the R-PDCCH region inslot 1.

Thus, DCI for terminal 200 under the control of base station 100 can betransmitted efficiently using R-PDCCH regions provided for DCI intendedfor relay stations.

In the pattern of the first search space configuration rule, the peakposition of the distribution of unit region candidates targeted fordecoding with respect to R-CCE aggregation level is located towardsgreater R-CCE aggregation levels as compared to the pattern of thesecond search space configuration rule.

Thus, efficient DCI transmission using an adequate number of RE groupsto satisfy the desired communication quality becomes possible.Consequently, it is also possible to prevent the blocking probabilityfrom increasing.

In terminal 200, PDCCH receiving section 207 configures a search spacebased on the search space configuration rule and performs blind-decodingon each of the plurality of unit region candidates targeted for decodingthat form the search space. Each unit region candidate targeted fordecoding is composed of one or more concatenated R-CCEs (control channelelements).

In a search space configuration rule, corresponding numbers of unitregion candidates targeted for decoding are respectively associated witha plurality of aggregation levels regarding CCEs. The first search spaceconfiguration rule for slot 0 and the second search space configurationrule for slot 1 have mutually different patterns regarding the numbersof unit region candidates targeted for decoding with respect to theplurality of aggregation levels regarding R-CCEs. In other words,patterns regarding the number of unit region candidates targeted fordecoding with respect to R-CCE aggregation level are independentlyspecified for the R-PDCCH region in slot 0 and the R-PDCCH region inslot 1.

Thus, DCI for terminal 200 under the control of base station 100 can bereceived efficiently using R-PDCCH regions provided for DCI intended forrelay stations.

In the description above, it was assumed that the numbers of REs perR-CCE were so related as to satisfy “slot 0<slot 1.” However, by way ofexample, if an R-PDCCH region of one RB's width is divided into two inslot 1, the relationship may also be “slot 0>slot 1” instead.Accordingly, if “slot 0>slot 1,” the terms slot 0 and slot 1 may bereversed in the description above. In essence, the embodiment deals withsearch space configuration rules for a first slot and a second slot, andit does not by any means impose any limitations as to which slots thefirst slot and the second slot are.

Embodiment 2

Embodiment 2 relates to another variation of the search spaceconfiguration rule. The base station and the terminal according toEmbodiment 2 share the same basic configurations as those inEmbodiment 1. Accordingly, a description will be provided referring backto FIGS. 9 and 10.

In base station 100 of Embodiment 2, configuration section 101configures a resource region used for the transmission of DCI forterminal 200. Candidates to be configured as the resource region includea PDCCH region, an R-PDCCH region of slot 0, and an R-PDCCH region ofslot 1.

Search space configuration section 103 configures a search space basedon the search space configuration rule associated with a configurationresource region indicated by configuration information fromconfiguration section 101. A search space configuration rule that isused when the resource region is an R-PDCCH region in slot 0 and asearch space configuration rule that is used when the resource region isan R-PDCCH region in slot 1 have mutually different patterns regardingthe number of unit region candidates targeted for decoding with respectto CCE aggregation level if the “coding rates” applied to slot 0 andslot 1 are different. In other words, the patterns regarding the numberof unit region candidates targeted for decoding with respect to CCEaggregation level are independently specified for the R-PDCCH region inslot 0 and the R-PDCCH region in slot 1 on the basis of the “codingrate” of each slot. The term coding rate as referred to in Embodiment 2and onward refers to a coding rate derived from the numbers of REs forthe same R-CCE aggregation level (e.g., per R-CCE) in slot 0 and slot 1.

Here, the search space configuration rules used for a slot of a lowcoding rate and a slot of a high coding rate are referred to as “firstsearch space configuration rule” and “second search space configurationrule,” respectively.

Variations of the “first search space configuration rule” and the“second search space configuration rule” are described below.

<Variation 6 of Search Space Configuration Rule>

FIG. 19 is a diagram illustrating variation 6 of the search spaceconfiguration rule. As shown in FIG. 19, when slot 0 has a higher codingrate than slot 1, the pattern of the first search space configurationrule is a pattern where, for CCE aggregation levels 1, 2, 4, and 8, thenumbers of unit region candidates targeted for decoding are 8, 2, 2, and0, respectively. On the other hand, the pattern of the second searchspace configuration rule is a pattern where, for CCE aggregation levels1, 2, 4, and 8, the numbers of unit region candidates targeted fordecoding are 0, 6, 4, and 2, respectively.

In this case, in order to obtain an adequate number of REs, if therequisite coding rate is high (i.e., low redundancy), the R-CCEaggregation levels need to be increased, whereas if the requisite codingrate is low (i.e., high redundancy), the R-CCE aggregation level needsto be decreased.

This requirement is met by variation 6 of the search space configurationrule mentioned above. Specifically, in variation 6 of the search spaceconfiguration rule, the patterns of the first search space configurationrule and the second search space configuration rule are determined inaccordance with the coding rate. Further, the peak position of thedistribution of unit region candidate groups targeted for decodingcontained in the search space with respect to R-CCE aggregation level islocated towards lesser R-CCE aggregation levels for the pattern of thefirst search space configuration rule than it is for the pattern of thesecond search space configuration rule.

The fact that “the peak position of the distribution of unit regioncandidate groups targeted for decoding with respect to R-CCE aggregationlevel is shifted towards lesser CCE aggregation levels for the patternof the first search space configuration rule than it is for the patternof the second search space configuration rule” signifies the mattersbelow.

<Matter 1> It signifies that the weighted average of the inverses of thecoding rates (i.e., redundancies) for the second search spaceconfiguration rule with respect to the number of blind decodingoperations becomes greater than it is for the first search spaceconfiguration rule. The weighted average of the inverses of coding rates(i.e., redundancies) with respect to the number of blind decodingoperations (i.e., the number of unit region candidates targeted fordecoding) is represented by Equation (3) below.

$\begin{matrix}{\left\lbrack {{Eq}.\mspace{14mu} 3} \right\rbrack\mspace{664mu}} & \; \\{X_{{Slot}\# n}^{\prime} = \frac{\begin{matrix}{\sum\limits_{R\text{-}{CCEaggregation}\mspace{14mu}{level}}^{\;}\left( {\left( {{coding}\mspace{20mu}{rate}\mspace{14mu}{per}\mspace{14mu} R\text{-}{CCE}\mspace{14mu}{{agg}.\mspace{14mu}{level}}} \right)^{- 1} \times} \right.} \\\left. \left( {\#\mspace{14mu}{of}\mspace{14mu}{blind}\mspace{14mu}{decoding}\mspace{14mu}{operations}} \right) \right)\end{matrix}}{\sum\limits_{R\text{-}{CCEaggregation}\mspace{14mu}{level}}^{\;}{\#\mspace{14mu}{of}\mspace{14mu}{blind}\mspace{14mu}{decoding}\mspace{14mu}{operations}}}} & (3)\end{matrix}$

Equation (3) may be modified as in Equation (4) below.

$\begin{matrix}{\left\lbrack {{Eq}.\mspace{14mu} 4} \right\rbrack\mspace{664mu}} & \; \\\begin{matrix}{X_{{Slot}\# n}^{\prime} = \frac{\begin{matrix}{\sum\limits_{R\text{-}{CCEaggregation}\mspace{14mu}{level}}^{\;}\left( {\left( {{coding}\mspace{20mu}{rate}\mspace{14mu}{per}\mspace{14mu} R\text{-}{CCE}\mspace{14mu}{{agg}.\mspace{14mu}{level}}} \right)^{- 1} \times} \right.} \\\left. \left( {\#\mspace{14mu}{of}\mspace{14mu}{blind}\mspace{14mu}{decoding}\mspace{14mu}{operations}} \right) \right)\end{matrix}}{\sum\limits_{R\text{-}{CCEaggregation}\mspace{14mu}{level}}^{\;}{\#\mspace{14mu}{of}\mspace{14mu}{blind}\mspace{14mu}{decoding}\mspace{14mu}{operations}}}} \\{= {\left( \frac{\left( {\#\mspace{14mu}{of}\mspace{14mu}{DCI}\mspace{14mu}{bits}} \right)}{\left( {\#\mspace{14mu}{of}\mspace{14mu}{REs}\mspace{14mu}{per}\mspace{14mu} R\text{-}{CCE}} \right) \times \left( {{mod}.\mspace{14mu}{level}} \right)} \right) \cdot}} \\{\left( {{weighted}\mspace{14mu}{{avg}.\mspace{14mu}{of}}\mspace{14mu} R\text{-}{CCE}\mspace{14mu}{{agg}.\mspace{14mu}{levels}}\mspace{14mu}{with}\mspace{14mu}{respect}} \right.} \\\left. {{to}\mspace{14mu}\#\mspace{14mu}{of}\mspace{14mu}{blind}\mspace{14mu}{decoding}\mspace{14mu}{operations}} \right)\end{matrix} & (4)\end{matrix}$

Accordingly, the weighted average of the inverses of coding rates withrespect to the number of blind decoding operations may also be describedas the product obtained by multiplying the inverse of the coding rateper R-CCE with the weighted average of R-CCE aggregation levels withrespect to the number of blind decoding operations.

<Matter 2> It signifies that the R-CCE aggregation level at which thenumber of unit region candidates targeted for decoding becomes greatestfor the first search space configuration rule is lower than it is forthe second search space configuration rule. If there are a plurality ofR-CCE aggregation levels at which the number of unit region candidatestargeted for decoding is greatest, it signifies that the average valueof the R-CCE aggregation levels at which the number of unit regioncandidates targeted for decoding is greatest is lower for the firstsearch space configuration rule than it is for the second search spaceconfiguration rule.

<Matter 3> It signifies that the weighted average of R-CCE aggregationlevels with respect to the number of blind decoding operations is lowerfor the first search space configuration rule than it is for the secondsearch space configuration rule.

<Matter 4> It signifies that the weighted average of R-CCE aggregationlevel indices with respect to the number of blind decoding operations islower for the first search space configuration rule than it is for thesecond search space configuration rule. R-CCE aggregation level indicesare numbered 0, 1, 2, 3 in ascending order of R-CCE aggregation level.With respect to R-CCE aggregation levels 1, 2, 4, and 8, their R-CCEaggregation level indices are defined as 0, 1, 2, and 3, respectively.

Assuming that the number of REs per R-CCE is 44 in slot 0 and 72 in slot1, that the number of DCI bits is 56 bits in slot 0 and 42 bits in slot1, and that the modulation level is QPSK, whether or not theabove-mentioned <Matter 1> to <Matter 4> are satisfied may specificallybe confirmed as follows.

<Matter 1>

The weighted average of the inverses of the coding rates with respect tothe number of blind decoding operations is (((56/(44×2)){circumflex over( )}(−1))×0+((56/(88×2)){circumflex over( )}(−1))×6+((56/(176×2)){circumflex over( )}(−1))×4+((56/(352×2)){circumflex over ( )}(−1))×2)/(0+6+4+2)≈5.76 inslot 0, and is (((42/(72×2)){circumflex over( )}(−1))×8+((42/(144×2)){circumflex over( )}(−1))×2+((42/(288×2)){circumflex over( )}(−1))×2+((42/(576×2)){circumflex over ( )}(−1))×0)/(8+2+2+0)≈5.71 inslot 1. Thus, the relationship “first search space configurationrule<second search space configuration rule” is satisfied.

<Matter 2>

The R-CCE aggregation level at which the number of blind decodingoperations becomes greatest is 2 for the second search spaceconfiguration rule, and 1 for the first search space configuration rule.Thus, the relationship “first search space configuration rule<secondsearch space configuration rule” is satisfied.

<Matter 3>

The weighted average of R-CCE aggregation levels with respect to thenumber of blind decoding operations is (1×0+2×6+4×4+8×2)/(0+6+4+2)≈3.67for the second search space configuration rule, and(1×8+2×2+4×2+8×0)/(8+2+2+0)≈1.67 for the first search spaceconfiguration rule. Thus, the relationship “first search spaceconfiguration rule<second search space configuration rule” is satisfied.

<Matter 4>

The weighted average of R-CCE aggregation level indices with respect tothe number of blind decoding operations is(0×0+1×6+2×4+3×2)/(0+6+4+2)≈1.67 for the second search spaceconfiguration rule, and (0×8+1×2+2×2+3×0)/(8+2+2+0)≈0.50 for the firstsearch space configuration rule. Thus, the relationship “first searchspace configuration rule<second search space configuration rule” issatisfied.

Allocating section 108 allocates the DCI to unit region candidatestargeted for decoding indicated by the search space information fromsearch space configuration section 103. The DCI is thus transmitted toterminal 200.

In terminal 200, if the region indicated by the search space regioninformation received from configuration information receiving section206 is an R-PDCCH region in slot 0 or an R-PDCCH region in slot 1, PDCCHreceiving section 207 performs blind decoding on the basis of the searchspace configuration rule corresponding to each. These rules correspondto the above-described rules adopted in base station 100.

According to the present embodiment, search space configuration section103 of base station 100, as described above, configures a search spacebased on the search space configuration rule corresponding to theR-PDCCH region of the slot to be configured.

If the coding rate configured for slot 1 is greater than the coding rateconfigured for slot 0, in the first search space configuration rule usedfor slot 0, the peak position of the distribution of unit regioncandidates targeted for decoding with respect to R-CCE aggregation levelis located towards lesser R-CCE aggregation levels as compared to thepattern of the second search space configuration rule used for slot 1.

Thus, efficient DCI transmission using an adequate number of RE groupsto satisfy the desired communication quality becomes possible.Consequently, it is also possible to prevent the blocking probabilityfrom increasing.

In the description above, it was assumed that the coding rates were sorelated as to satisfy “slot 0>slot 1.” However, by way of example, if anR-PDCCH region of one RB's width is divided into two in slot 1, or ifthe number of DCI bits in slot 0 is less than that in slot 1 (e.g., ifDCI format 1C is assigned to slot 0 so that it is 28 bits), therelationship may also be “slot 0<slot 1” instead. Accordingly, if “slot0<slot 1,” the terms slot 0 and slot 1 may be reversed in thedescription above. In essence, the embodiment deals with search spaceconfiguration rules for a first slot and a second slot, and it does notby any means impose any limitations as to which slots the first slot andthe second slot are.

Embodiment 3

In Embodiment 3, a plurality of types of DCI bit counts allocatable tothe R-PDCCH region per slot are defined. The base station and theterminal according to Embodiment 3 share the same basic configurationsas those in Embodiment 1. Accordingly, a description will be providedreferring back to FIGS. 9 and 10.

In base station 100 of Embodiment 3, configuration section 101configures a resource region used for the transmission of DCI forterminal 200. Candidates of resource regions to be configured include aPDCCH region, an R-PDCCH region of slot 0, and an R-PDCCH region of slot1.

Search space configuration section 103 configures a search space basedon the search space configuration rule associated with a configurationresource region indicated by configuration information fromconfiguration section 101. A search space configuration rule that isused when the resource region is an R-PDCCH region in slot 0 and asearch space configuration rule that is used when the resource region isan R-PDCCH region in slot 1 have patterns regarding the number of unitregion candidates targeted for decoding with respect to CCE aggregationlevel that mutually differ based on “any one value that falls betweenthe minimum value and the maximum value that the coding rate mayassume.” In other words, the patterns regarding the number of unitregion candidates targeted for decoding with respect to CCE aggregationlevel are independently specified for the R-PDCCH region in slot 0 andthe R-PDCCH region in slot 1 on the basis of the “any one value thatfalls between the minimum value and the maximum value that the codingrate may assume.” What is meant by “any one value that falls between theminimum value and the maximum value that the coding rate may assume” is,for example, a coding rate average. For purposes of brevity, adescription will be provided below using a coding rate average.

For the case at hand, search space configuration rules employed for aslot with a low coding rate average and a slot with a high coding rateaverage will be referred to as the “first search space configurationrule” and the “second search space configuration rule,” respectively.The term “coding rate average” refers to the average of a plurality oftypes of coding rates in cases where a plurality of types of DCI bitcounts are defined. In addition, the expression “the defined DCI bitcounts” refers to all types of DCI bit counts that may be allocated tothe R-PDCCH region, and not to the DCI bit count that is actuallyallocated to each R-PDCCH region. Accordingly, if, for example, 42 bitsand 56 bits are allocatable as DCI bit counts in slot 0, both 42 bitsand 56 bits are used to calculate the coding rate average even if theDCI bit count that is actually allocated to the R-PDCCH region is 42bits alone.

Variations of the “first search space configuration rule” and the“second search space configuration rule” are described below.

<Variation 7 of Search Space Configuration Rule>

FIG. 20 is a diagram illustrating variation 7 of the search spaceconfiguration rule. As shown in FIG. 20, when slot 0 has a higher codingrate average than slot 1, the pattern of the first search spaceconfiguration rule is a pattern where, for CCE aggregation levels 1, 2,4, and 8, the numbers of unit region candidates targeted for decodingare 8, 2, 2, and 0, respectively. On the other hand, the pattern of thesecond search space configuration rule is a pattern where, for CCEaggregation levels 1, 2, 4, and 8, the numbers of unit region candidatestargeted for decoding are 1, 6, 3, and 2, respectively.

In other words, in variation 7 of the search space configuration rule,the patterns of the first search space configuration rule and the secondsearch space configuration rule are determined in accordance with thecoding rate average. The peak position of the distribution of unitregion candidate groups targeted for decoding contained in the searchspace with respect to R-CCE aggregation level is located towards lesserR-CCE aggregation levels for the pattern of the first search spaceconfiguration rule than it is for the pattern of the second search spaceconfiguration rule.

The fact that “for the pattern of the first search space configurationrule, the peak position of the distribution of unit region candidategroups targeted for decoding with respect to R-CCE aggregation level isshifted towards lesser CCE aggregation levels than it is for the patternof the second search space configuration rule” signifies the mattersbelow.

<Matter 1> It signifies that the weighted average of the inverses of thecoding rate averages (i.e., redundancies) with respect to the number ofblind decoding operations is greater for the second search spaceconfiguration rule than it is for the first search space configurationrule. The weighted average of the inverses of the coding rate averages(i.e., redundancies) with respect to the number of blind decodingoperations (i.e., the number of unit region candidates targeted fordecoding) is represented by Equation (5) below:

$\begin{matrix}\left\lbrack {{Eq}.\mspace{14mu} 5} \right\rbrack & \; \\{X_{{Slot}\# n}^{''} = \frac{\begin{matrix}{\sum\limits_{R\text{-}{CCEaggregation}\mspace{14mu}{level}}^{\;}\left( {\left( {{avg}.\left( {{coding}\mspace{20mu}{rate}\mspace{14mu}{per}\mspace{14mu} R\text{-}{CCE}\mspace{14mu}{{agg}.\mspace{14mu}{level}}} \right)} \right)^{- 1} \times} \right.} \\\left. \left( {\#\mspace{14mu}{of}\mspace{14mu}{blind}\mspace{14mu}{decoding}\mspace{14mu}{operations}} \right) \right)\end{matrix}}{\sum\limits_{R\text{-}{CCEaggregation}\mspace{14mu}{level}}^{\;}{\#\mspace{14mu}{of}\mspace{14mu}{blind}\mspace{14mu}{decoding}\mspace{14mu}{operations}}}} & (5)\end{matrix}$

Equation (5) may be modified as in Equation (6) below.

$\begin{matrix}{\left\lbrack {{Eq}.\mspace{14mu} 6} \right\rbrack\mspace{664mu}} & \; \\\begin{matrix}{X_{{Slot}\# n}^{''} = \frac{\begin{matrix}\begin{matrix}\sum\limits_{R\text{-}{CCEaggregation}\mspace{14mu}{level}}^{\;} \\\left( \left( {{{avg}.\left( {{coding}\mspace{20mu}{rate}\mspace{14mu}{per}\mspace{14mu} R\text{-}{CCE}\mspace{14mu}{{agg}.\mspace{14mu}{level}}} \right)^{- 1}} \times} \right. \right.\end{matrix} \\\left. \left( {\#\mspace{14mu}{of}\mspace{14mu}{blind}\mspace{14mu}{decoding}\mspace{14mu}{operations}} \right) \right)\end{matrix}}{\sum\limits_{R\text{-}{CCEaggregation}\mspace{14mu}{level}}^{\;}{{number}\mspace{14mu}{of}\mspace{14mu}{blind}\mspace{14mu}{decoding}\mspace{14mu}{operations}}}} \\{= {\left( {{avg}.\frac{\left( {{DCI}\mspace{14mu}{bit}\mspace{14mu}{count}} \right)}{\left( {\#\mspace{14mu}{of}\mspace{14mu}{REs}\mspace{14mu}{per}\mspace{14mu} R\text{-}{CCE}} \right) \times \left( {{mod}.\mspace{14mu}{level}} \right)}} \right)^{- 1} \cdot}} \\{\left( {{weighted}\mspace{14mu}{{avg}.\mspace{14mu}{of}}\mspace{14mu} R\text{-}{CCE}\mspace{14mu}{{agg}.\mspace{14mu}{levels}}\mspace{14mu}{with}\mspace{14mu}{respect}} \right.} \\\left. {{to}\mspace{14mu}\#\mspace{14mu}{of}\mspace{14mu}{blind}\mspace{14mu}{decoding}\mspace{14mu}{operations}} \right)\end{matrix} & (6)\end{matrix}$

Accordingly, the weighted average of the inverses of the coding rateaverages (redundancies) with respect to the number of blind decodingoperations may also be described as the product obtained by multiplyingthe inverse of the coding rate average per R-CCE with the weightedaverage of R-CCE aggregation levels with respect to the number of blinddecoding operations.

<Matter 2> It signifies that the R-CCE aggregation level at which thenumber of unit region candidates targeted for decoding becomes greatestfor the first search space configuration rule is lower than it is forthe second search space configuration rule. If there are a plurality ofR-CCE aggregation levels at which the number of unit region candidatestargeted for decoding is greatest, it signifies that the average valueof the R-CCE aggregation levels at which the number of unit regioncandidates targeted for decoding is greatest is lower for the firstsearch space configuration rule than it is for the second search spaceconfiguration rule.

<Matter 3> It signifies that the weighted average of R-CCE aggregationlevels with respect to the number of blind decoding operations is lowerfor the first search space configuration rule than it is for the secondsearch space configuration rule.

<Matter 4> It signifies that the weighted average of R-CCE aggregationlevel indices with respect to the number of blind decoding operations islower for the first search space configuration rule than it is for thesecond search space configuration rule. R-CCE aggregation level indicesare numbered 0, 1, 2, 3 in ascending order of R-CCE aggregation level.With respect to R-CCE aggregation levels 1, 2, 4, and 8, their R-CCEaggregation level indices are defined as 0, 1, 2, and 3, respectively.

Assuming that the number of REs per R-CCE is 44 in slot 0 and 72 in slot1, that the number of DCI bits is 42 bits and 56 bits in slot 0 and 42bits in slot 1, and that the modulation level is QPSK, whether or notthe above-mentioned <Matter 1> to <Matter 4> are satisfied mayspecifically be confirmed as follows.

<Matter 1>

The weighted average of the inverses of the coding rate averages withrespect to the number of blind decoding operations is((((42+56)/2/(44×2)){circumflex over( )}(−1))×1+(((42+56)/2/(88×2)){circumflex over( )}(−1))×6+(((42+56)/2/(176×2)){circumflex over( )}(−1))×3+(((42+56)/2/(352×2)){circumflex over( )}(−1))×2)/(1+6+3+2)≈6.14 in slot 0, and is (((42/(72×2)){circumflexover ( )}(−1))×8+((42/(144×2)){circumflex over( )}(−1))×2+((42/(288×2)){circumflex over( )}(−1))×2+((42/(576×2)){circumflex over ( )}(−1))×0)/(8+2+2+0)≈5.71 inslot 1. Thus, the relationship “first search space configurationrule<second search space configuration rule” is satisfied.

<Matter 2>

The R-CCE aggregation level at which the number of blind decodingoperations becomes greatest is 2 for the second search spaceconfiguration rule, and 1 for the first search space configuration rule.Thus, the relationship “first search space configuration rule<secondsearch space configuration rule” is satisfied.

<Matter 3>

The weighted average of R-CCE aggregation levels with respect to thenumber of blind decoding operations is (1×1+2×6+4×3+8×2)/(1+6+3+2)≈3.42for the second search space configuration rule, and(1×8+2×2+4×2+8×0)/(8+2+2+0)≈1.67 for the first search spaceconfiguration rule. Thus, the relationship “first search spaceconfiguration rule<second search space configuration rule” is satisfied.

<Matter 4>

The weighted average of R-CCE aggregation level indices with respect tothe number of blind decoding operations is(0×1+1×6+2×3+3×2)/(1+6+3+2)≈1.50 for the second search spaceconfiguration rule, and (0×8+1×2+2×2+3×0)/(8+2+2+0)≈0.50 for the firstsearch space configuration rule. Thus, the relationship “first searchspace configuration rule<second search space configuration rule” issatisfied.

Allocating section 108 allocates the DCI to unit region candidatestargeted for decoding indicated by the search space information fromsearch space configuration section 103. The DCI is thus transmitted toterminal 200.

In terminal 200, if the region indicated by the search space regioninformation received from configuration information receiving section206 is an R-PDCCH region in slot 0 or an R-PDCCH region in slot 1, PDCCHreceiving section 207 performs blind decoding on the basis of the searchspace configuration rule corresponding to each region. These rulescorrespond to the above-described rules adopted in base station 100.

According to the present embodiment, search space configuration section103 of base station 100, as described above, configures a search spacebased on the search space configuration rule corresponding to theR-PDCCH region of the slot to be configured.

If the average coding rate configured for slot 1 is greater than theaverage coding rate configured for slot 0, in the first search spaceconfiguration rule used for slot 0, the peak position of thedistribution of unit region candidates targeted for decoding withrespect to R-CCE aggregation level is located towards lesser R-CCEaggregation levels as compared to the pattern of the second search spaceconfiguration rule used for slot 1.

Thus, efficient DCI transmission using an adequate number of RE groupsto satisfy the desired communication quality becomes possible.Consequently, it is also possible to prevent the blocking probabilityfrom increasing.

In the description above, it was assumed that the coding rates were sorelated as to satisfy “slot 0>slot 1.” However, by way of example, if anR-PDCCH region of one RB's width is divided into two in slot 1, or ifthe number of DCI bits in slot 0 is less than that in slot 1 (e.g., ifDCI format 1C is assigned to slot 0 so that it is 28 bits), therelationship may also be “slot 0<slot 1” instead. Accordingly, if “slot0<slot 1,” the terms slot 0 and slot 1 may be reversed in thedescription above. In essence, the embodiment deals with search spaceconfiguration rules for a first slot and a second slot, and it does notby any means impose any limitations as to which slots the first slot andthe second slot are.

The description above involved coding rate “averages.” However, it mayinstead range from a lower limit value to an upper limit value for aplurality of coding rates that are averaged. Specifically, it is assumedthat the number of REs per R-CCE is 44 in slot 0, and 72 in slot 1. Itis assumed that the number of DCI bits is 42 bits and 56 bits in slot 0,and 42 bits in slot 1. It is assumed that the modulation level is QPSK(2) for both. In this case, the lower limit value for the coding rate ofslot 0 is 42/(44×2)≈0.48. The upper limit value for the coding rate ofslot 0 is 56/(44×2)≈0.634. The lower limit value and upper limit valuefor the coding rate of slot 1 are equal to each other at 42/(72×2)≈0.29.

Other Embodiments

(1) In variations 1-7 of the search space configuration rule describedin the embodiments above, examples were given where, for both the firstsearch space configuration rule and the second search spaceconfiguration rule, the peak position of the distribution of unit regioncandidate groups targeted for decoding contained in the search spacewith respect to R-CCE aggregation level is located off-center towardseither lesser or greater R-CCE aggregation levels. However, the claimedinvention is by no means limited as such, and instead, the peak positionof one of the first search space configuration rule and the secondsearch space configuration rule may be located on the lesser side whilethe peak position of the other is located on the greater side. By thususing such search space configuration rules where peak positions differsignificantly between the first slot and the second slot, the basestation is able to flexibly allocate DCI even under a fluctuatingpropagation environment.

(2) In the foregoing embodiments, descriptions were provided withrespect to the R-PDCCH regions of slot 0 and slot 1 within the samesubframe. However, the claimed invention is by no means limited as such,and is also applicable to a plurality of R-PDCCH regions that are offsetby at least one slot time-wise. In addition, it is also applicable to aplurality of R-PDCCH regions that are offset by at least one RBfrequency-wise. It is also applicable to a plurality of R-PDCCH regionsthat are offset by at least one slot and at least one RB time-wise andfrequency-wise, respectively.

(3) In the foregoing embodiments, descriptions were provided assumingQPSK for the modulation scheme of the R-PDCCH. However, the claimedinvention is by no means limited as such, and is also applicable tocases where the modulation scheme for the R-PDCCH is some scheme otherthan QPSK.

(4) In the foregoing embodiments, descriptions were provided withrespect to antennas. However, the claimed invention is similarlyapplicable to antenna ports.

The term “antenna port” refers to a logical antenna including one ormore physical antennas. In other words, the term “antenna port” does notnecessarily refer to a single physical antenna, and may sometimes referto an array antenna including a plurality of antennas, and/or the like.

For example, 3GPP LTE does not specify the number of physical antennasin an antenna port, but specifies an antenna port as a minimum unit inwhich a base station can transmit different reference signals.

An antenna port may also be specified as a minimum unit by whichweightings of precoding vectors are multiplied.

(5) In the foregoing embodiments, the claimed invention is configuredwith hardware by way of example, but the claimed invention may also beprovided by software in cooperation with hardware.

The functional blocks used in the descriptions of the foregoingembodiments may typically be implemented as an LSI, which is anintegrated circuit. They may be individual chips, or some of or all ofthem may be integrated into a single chip. The term “LSI” is used here,but the terms “IC,” “system LSI,” “super LSI,” or “ultra LSI” may alsobe adopted depending on the degree of integration.

Alternatively, circuit integration may also be implemented using adedicated circuit or a general-purpose processor other than an LSI. AnFPGA (field programmable gate array) which is programmable after LSImanufacturing, or a reconfigurable processor which allowsreconfiguration of connections and settings of circuit cells in an LSImay be used.

Should a circuit integration technology replacing LSI appear as a resultof advancements in semiconductor technology or other derivativetechnology, the functional blocks could be integrated using such atechnology. Biotechnology applications, and/or the like, are conceivableprospects.

The disclosure of the specification, the drawings, and the abstractincluded in Japanese Patent Application No. 2010-164309, filed on Jul.21, 2010, is incorporated herein by reference in its entirety.

INDUSTRIAL APPLICABILITY

The base station, terminal, transmission method, and reception method ofthe claimed invention are useful in that they are capable of efficientlytransmitting downlink allocation control information.

REFERENCE SIGNS LIST

-   100 base station-   101 configuration section-   102 control section-   103 search space configuration section-   104 PDCCH generating section-   105, 106, 107 coding/modulating section-   108 allocating section-   109 multiplexing section-   110, 213 IFFT section-   111, 214 CP adding section-   112, 215 RF transmitting section-   113, 201 antenna-   114, 202 RF receiving section-   115, 203 CP removing section-   116, 204 FFT section-   117 extracting section-   118 IDFT section-   119 data receiving section-   120 ACK/NACK receiving section-   131 transmission region configuration section-   132 transmission mode configuration section-   200 terminal-   205 demultiplexing section-   206 configuration information receiving section-   207 PDCCH receiving section-   208 PDSCH receiving section-   209, 210 modulating section-   211 DFT section-   212 mapping section

The invention claimed is:
 1. An integrated circuit comprising: at leastone input which, in operation, receives an input signal; a controlcircuitry coupled to the at least one input, which, in operation,controls: reception of downlink control information that is mapped to atleast one of a first search space or a second search space, wherein thefirst search space includes a plurality of first decoding regioncandidates, each corresponding to any one of first control channelelement (CCE) aggregation levels, and the second search space includes aplurality of second decoding region candidates, each corresponding toany one of second CCE aggregation levels, wherein a weighted average ofCCE aggregation levels with respect to a number of decoding regioncandidates included in the first search space is greater than that ofthe second search space, and the weighted average is calculated bydividing a sum of the products of CCE aggregation levels andcorresponding number of decoding region candidates by a sum of thenumber of decoding region candidates for each search space; andblind-decoding of the plurality of first decoding region candidates andthe plurality of second decoding region candidates to acquire thedownlink control information.
 2. The integrated circuit according toclaim 1, wherein the first search space and the second search space areconfigured in an extended downlink control channel on a data region. 3.The integrated circuit according to claim 1, wherein the first searchspace and the second search space are terminal specific search spaces(UE-specific search spaces).
 4. The integrated circuit according toclaim 1, wherein the control circuitry controls reception of higherlayer signaling information which indicates a resource region used totransmit the downlink control information.
 5. The integrated circuitaccording to claim 1, wherein the control circuitry controls receptionof higher layer signaling information which indicates a subframe onwhich the first search space or the second search space is configured.6. The integrated circuit according to claim 1, wherein multiple sets ofrelationship between the CCE aggregation level and the number ofdecoding region candidates are defined for each of the first searchspace and the second search space.
 7. The integrated circuit accordingto claim 1, wherein the received downlink control information includescontrol information for each of a plurality of terminal apparatuses. 8.The integrated circuit according to claim 1, wherein the second CCEaggregation levels overlap with the first CCE aggregation levels andinclude at least one aggregation level smaller than any of the first CCEaggregation levels.
 9. The integrated circuit according to claim 1,wherein a number of resource elements (REs) that compose one CCE of thefirst search space is smaller than that of the second search space.